I tried 5 builds so far via Jenkins, all resulted in failure, solved a few configuration issues to resolve problems, and now I'm facing an issue that has to do with keychains. Tried to follow this thread to figure out the appropriate action.

And I completely turned off the git checkout process in the Jenkin's job configuration just to be safe ... although I should have been able to get away by simply ignoring submodules too but why checkout when I don't need to.

It should have already been working based on the directions from the RestKit website:
Add the following Header Search Paths (including the quotes):

"$(BUILT_PRODUCTS_DIR)/../../Headers"

But I suppose for some reason that meant one thing to Xcode and something entirely different to jenkins-xcode-plugin.
So through trial and error and watching the logs, I figured out that I needed to add:

"$(BUILT_PRODUCTS_DIR)/../my_project/Build/Headers

in order for jenkins-xcode-plugin to pick it up and work with it properly.